Devices for testing communication networks such as telephone or data systems by simulating calls through exchanges or trunks are well known. Generally, such simulators are adapted to rapidly apply the sequence of call signals through the circuits of an exchange and test the responses thereto. In this way, the operation of the exchange is evaluated and faulty equipment identified without interrupting subscriber service.
U.S. Pat. No. 4,021,624 issued to Kelly et al, May 3, 1977, discloses an automatic call generator connectable with the main distribution frame of a common control telephone system that monitors the operation of the system. The automatic call generator is connected to dedicated line and trunk circuit ports and attempts to place calls from one dedicated spot to another. If the system fails to terminate a call within a prescribed period of time, a malfunction is noted. Two malfunctions within a prescribed set of programs for monitoring the system cause a system alarm to be generated. The call generator also tests itself after proceeding through assigned programs for monitoring the system.
U.S. Pat. No. 4,238,649 issued to Marc Kemler, Dec. 9, 1980, discloses a traffic simulator for tandem exchange testing. The simulator comprises a calling side module to simulate a calling exchange with facilities for the selection of dialing information, type of test operation and signaling code. The calling side module is connected to the tandem exchange at an i/c circuit terminating equipment of a type suited to the selected signaling code. An answering side module connected to the tandem exchange at an o/g circuit terminating equipment simulates a called exchange and comprises means for selection of the signaling code for communication with the terminating equipment. The two modules are independent and a signal flows between them passing exclusively through the tandem exchange.
U.S. Pat. No. 4,255,625 issued to Walton et al, Mar. 10, 1981, discloses a call processing monitor system for dynamically verifying the operation of a telephone switching center. The system provides for continuously testing a telephone switching center's ability to process telephone traffic by placing telephone calls one at a time from various network inlets to various network outlets in the switching center. Upon detection of a predetermined number of consecutive failures, an output alarm signal is generated by the system.
U.S. Pat. No. 4,467,148 issued to Stafford et al, Aug. 21, 1984, discloses a telephone line analyzer that provides automatic attenuation measurement of tie trunk lines and other telephone lines through measurement of the electrical level of a tone responder. The analyzer is primarily directed to testing telephone lines interconnected between trunk line selectable computerized private branch exchanges (PBXs) of the same user. The analyzer automatically dials a remote PBX through a desired tie trunk line, activates a remote tone responder, and measures and records the test results. The analyzer may also perform echo return loss measurements.
The testing arrangements described in the aforementioned patents provide periodic tests that assure the integrity of portions of a network. Such testing is generally effective to provide adequate service to subscribers. There are malfunctions, however, that occur sporadically. Although these occurrences are uncommon, they may occur repeatedly on particular calls and thereby seriously affect a particular subscriber. Cut-off of an already established connection through a network is usually solved by a subscriber by redialing. Repeated cut-offs on calls between particular subscribers or areas, however, are evidence of degraded service that requires correction. The problem may be caused by marginal equipment in the particular network configuration used in the connection. The aforementioned arrangements are not adapted to determine the source of such malfunctions. It is an object of the invention to provide improved detection of cut-off in a network to facilitate corrective action.